feedback on my neighbour's model

First of all, he uses sandbox to create the surrounding landscape, which is super cool and I don't know how to do it. And his work is full of geometry things, like each element is in different shapes, turning the work funny and eye-catching.
Besides, he apply materials to all those building elements, thus the whole building look realistic and stunning.
One thing I am a little confused is that there isn't a flat platform within the building for individuals to walk on despite those stairs (maybe he hasn't completed), and for the whole work I still find it super attracting and inspiring.